In a steam-electric power plant, high energy steam is produced by either a boiler, steam generator or nuclear reactor. This high pressure, high temperature steam is conveyed by piping to a steam turbine. Here the energy of the flowing steam acts on blades in order to rotate the turbine shaft that is directly connected to an electrical generator which produces the power for homes, hospitals, schools and industry. Exhaust steam from the turbine is condensed into water in the condenser and is pumped back to the steam generator, boiler or reactor where the cycle is repeated. All steam fossil fired and nuclear power plants follow this basic cycle called the Rankine cycle in honor of a famous, early thermodynamacist.
This invention is directed to apparatus installed in the power plant condenser now described in detail.
The spent, low energy steam flows from the exhaust of the turbine into a large heat exchanger called a surface condenser where, as the name implies, the steam is condensed. In the large sizes associated with 1000MW plants, the condenser is as large as a church. Inside the condenser shell there are thousands of small diameter thin tubes that extend from a cold water inlet to a warm water outlet. The tubes are connected at their ends through tubesheets to chambers called waterboxes. The tubes are arrayed in forms with distinct patterns called tube bundles. A large quantity of cooling water flows through the tubes in order to condense the steam and continually carry away the heat of condensation to a source like a river, lake, ocean or cooling tower. The exhaust steam from the turbine enters the entire periphery of the tube bundles in a non-uniform, radial way and flows toward the center of each tube bundle through the immense number of tubes, condensing as it goes toward the air cooler section. The air cooler section extends along the length of the condenser between tube sheets.
In the air cooler, the last of the steam is condensed, non-condensable gases with some associated remaining steam vapor are collected along the length of the tube bundle and induced to flow to the cold water inlet end of the condenser. There all the non-condensable gases are discharged from air cooler section into the piping connected to air removal equipment.
Meanwhile, the condensate falls by gravity into the lower section of the condenser called a hotwell. But since the steam velocities in the condenser are of hurricane magnitudes (though at a low pressure and density) of from 50 to 400 ft/sec, as it drops, the steam is also pushed toward the vertical center of the condenser by the latter horizontal dynamic forces. To prevent tube vibration and provide support against the many categories of force loadings the tubes and the condenser must carry, all the tubes run through a multitude of support plates at intervals of from 2 to 4 ft. along their length. Like the tubesheets at the ends of the tubes, these plates are drilled to reflect the precise pattern of the tube bundles.
Condenser and turbine performances are interconnected. For a particular set of cooling water conditions, i.e., the temperature and flow rate available, and depending on the overall heat transfer coefficient of the condenser, amount of active tube surface and the steam to be condensed from the turbine, the condenser pressure will be established. Except for a small pressure loss, the condenser pressure essentially defines turbine backpressure. And turbine backpressure in turn determines the power the turbine produces at that time for a specific turbine inlet pressure and temperature (throttle condition). The condenser pressure has a surprising large impact on a typical steam turbine and effects its produced power by 1% to 3% for a change of 1 in. of hg (0.491 psi) in absolute pressure. In these days of heightened awareness of conservation of energy, it is important to operate and maintain a condenser backpressure as low as possible under all conditions.
In the distant past, through the 1940s and 1950s, condensers were of a modest size because the plants they served were usually of no more than 100 to 150 MW. However, with requirements for larger and larger plants though the late 1960s to the 1980s and with the advent of nuclear plants and their higher quantities of steam and large size, condensers also grew, usually by an untested, rapid, simple size extrapolation. Some condenser designs worked well; some did not perform as well, particularly after design extrapolations to much larger sizes. Because of the major size of a condenser, the past difficulty in conducting accurate tests, and the fact that utilities were regulated so that the extra costs could be passed through to the rate payers, any shortcoming in condenser performance was accepted provided the condenser operated reliably. In the late 1980s and through the 1990s there was little demand for power and during that period many of the companies that manufactured condensers ceased operation, letting go their design personnel and closing the doors. The utilities at this point were on their own if improvements in existing condensers performance were considered. Utilities as a rule did not have personnel possessing a sufficient detailed condenser design background in this equipment to take an effective action. The situation today is no different.
The field performance improvements represented by this invention apparatus provides improvement to large condensers, increases the thermal efficiency of the affected plants and thereby contributes to conserving energy. The invention improvement method and apparatus are based on our previous condenser design background at a major manufacturer and the inventors' observations and tests in the field over the past 40 years.